A comparative study on protective effect of optical nerve between crocin and erigeron breviscapus in chronic ocular hypertensive rats

Abstract

Background The primary cause of glaucomatous optic nerve damage is apoptosis of nerve cell and disorder of retinal circulation.Erigeron breviscapus is confirmed to have a protective effect on retinal ganglion cells (RGCs) in rats with chronic ocular hypertension, and crocin has the effect of anti-inflammation and anti-apoptosis.However, whether crocin can protect RGCs against ocular hypertension damage is unclear. Objective This study was to investigate the protective effect of crocin on the optic nerve in chronic ocular hypertension. Methods Thirty-two SD rats were randomized into the sham operation group, model control group, erigeron group and crocin group, 8 rats for each group.The right eyes served as experimental eyes.Chronic ocular hypertensive models were established by episcleral vein cauterization in the rats of the model control group, erigeron group and crocin group, and only conjunctiva was cut off in the sham operation group.Erigeron (150 mg/kg) and crocin (20 mg/kg) was intraperitoneally injected in the erigeron group and crocin group respectively 30 minutes before operation and once daily after operation for 4 weeks, and 0.5 ml normal saline was used in the sham operation group and model control group.Intraocular pressure (IOP) was measured before surgery and 1 day, 3 days, 1 week, 2 weeks, 3 weeks and 4 weeks after surgery.The samples of eyeballs and optic nerve in the rats were prepared at 4 weeks after surgery.Retinal thickness was measured by hematoxylin and eosin staining.The apoptosis of RGCs was detected by TUNEL assay.The ultrastructure change of optic nerve was examined under the transmission electron microscope, and the expression of bcl-2 and bax proteins in retinal homogenates was analyzed by Western blot.The use and care of the animals followed the Regulations for the Administration of Affair Concerning Experimental Animals by State Science and Technology Committee. Results The IOPs were significantly elevated in the model control group, erigeron group and crocin group in comparison with the sham operation group, and the IOPs was significantly higher in various time points after surgery than that before surgery (Fgroup=169.079, P=0.000; Ftime=50.505, P=0.000). The retinal thickness was (192.72±4.28), (165.15±3.89), (177.75±3.35) and (182.48±4.12)μm in the sham operation group, model control group, erigeron group and crocin group, and rat retinal thickness in the crocin group was significantly lower than that in the sham operation group and higher than that in model control group and erigeron group (all at P<0.05). The percentage of apoptotic RGCs in the sham operation group, model control group, erigeron group and crocin group, showed significant reduction in comparison with the model control group and erigeron group (all at P<0.05). The number of myelinated nerve fibers and bcl-2/bax values were significantly increased in the crocin group compared with the model control group and erigeron group (all at P<0.05). Conclusions Crocin affords a optic nerve by inhibiting RGC apoptosis and optic nerve degeneration in SD rats with chronic ocular hypertension, and the protecting effect of crocin is more prominent than that of erigeron breviscapus. Key words: Crocus/chemistry; Herbal medicine; Plant extracts/pharmacology; Ocular hypertension; Apoptosis; Retinal ganglion cells; Erigeron/chemistry; Optic nerve protection